Ultrastructural changes in presynaptic terminals following stimulation will be examined in ciliary ganglia from 3-4 day chicks which have been axotomized on the day of hatching. These changes will be compared with those occurring in normal ganglia of the same age. In addition, the effect of guanidine on synaptic transmission in ciliary ganglia will be studied, with intracellular recording from both presynaptic terminals and postsynaptic ganglion cells. The role of divalent cations in transmitter release at the neuromuscular junction will be examined by treating presynaptic terminals with the ionophore A23187 and applying Ca, Mg, Ba, Sr and Cd iontophoretically to the terminals to determine their relative efficacy in the release process. Further studies will be made on the effects of ionic strenth on the acetylcholine - induced permeability increases at the motor end-plate. This will be done by measuring reversal potentials for post-junctional currents produced by iontophoretic application of acetylcholine in solutions of varying Na/K concentration ratios and ionic strengths. BIBLIOGRAPHIC REFERENCES: Martin, A.R. (1976). The effect of membrane capacitance on nonlinear summation of synaptic potentials. J. Theoret. Biol. 59, 179-188. Martin, A.R. (1976). Current concepts of pre- and post-junctional mechanisms of neuromuscular transmission. Ann. N.Y. Acad. Sci. 274, 3-5.